Synthesis of supported immiscible nanoalloy catalysts via gas-switching reduction in the impregnation method

Abstract

Supported catalysts are widely used in chemical processes. For preparing supported catalysts, impregnation methods are recognized as straightforward procedures. Although the development of high-performance supported catalysts using impregnation methods is under consideration for various chemical reactions, there is a need for technologies that improve catalytic performance by exploiting the divergent physicochemical properties of active metals. In this study, we focused on alloying active metals to exploit their divergent properties and produced a simple impregnation-based alloy of immiscible rhodium, palladium, and platinum supported on alumina. Previous alloying methods have depended on elaborate and rigid procedures to control crystallization. However, we integrated the key alloying principles found in previous studies into a heat-treatment process of impregnation and developed a “gas-switch-triggered reduction method” in which all metal cations are simultaneously reduced by simply switching the treatment gas at a certain temperature. We applied the developed method to the alumina-supported ternary rhodium–palladium–platinum system. Alloying active metals led to 18 times higher catalytic performance in nitrile hydrogenation than that of the monometallic catalysts. The developed method requires no special equipment or procedures such as those used in previous studies and can be merged into the pretreatment process before catalyst evaluation using a continuous gas flow system, where in situ alloy formation occurs without the oxidation of the alloyed metals because of the absence of air exposure. The successful realization of the simple impregnation-based alloying method accelerates catalyst design based on the differences of the crystalline nature by random alloying and provides a bridge to their industrial application.